World first superconducting DC power transmission system a step closer

March 8, 2010 by Lin Edwards report
Superconducting cable. Image credit: Nano-Optics Energy

( -- A group of researchers in Japan have succeeded for the first time in superconducting power transmission of direct current over two hundred meters.

The researchers, from Nano-Optonics Energy Inc., and Chubu University’s Superconductivity and Sustainable Energy Center conducted their experiment as part of Nano-Optics Energy’s Superconducting DC Power Transmission Project.

The transmission loss of superconducting DC (alternating current) power transmission is ten times less than that of superconducting AC power transmission, and thirty times less than the transmission loss of ordinary AC power transmission. Since superconducting DC power reduces transmission loss, it could significantly reduce the amount of electricity that needs to be generated, if it could be used to replace normal AC power.

With the current emphasis on lower carbon emissions, the idea is attracting a great deal of attention, not only because less electricity would be needed, but also because alternative methods such as solar and wind power generate direct current, which in the present system has then to be converted to alternating current. Using direct current would also reduce the losses that occur during the conversion process.

The system being developed uses a liquid nitrogen circulation system, an adiabatic double tube, and a newly developed type of superconducting cable. Other new technologies developed by the researchers for the new system include a new method of thermally insulating the ends of the cable. This method, called the Peltier Current Lead (PCL), drastically cuts heat transfer between the cooling system and the ambient temperature section.

Direct current power transmission also has the advantage over AC of being cheaper and more efficient when transmitted over distances of 300 km and above. Superconducting power transmission theoretically has zero , and larger current power transmission is possible and over much longer distances, with transmission over distances as great as 10,000 km being feasible.

Nano-Optonics Energy collaborates with Chubu University on a number of basic technology projects and research into developing more efficient batteries. Their aim is to develop the most efficient and largest current transmission system in the world, using high-temperature DC superconductors.

Explore further: Superconductors for electrical, defense, space, medical applications

More information: Nano-Optonics Energy --

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2 / 5 (4) Mar 08, 2010
how much power does it take to keep all that cable cooled so low? disregarding potential leaks that would bring the dc system to a grinding halt, is it worth it in the cost of cooling liquid nitrogen down. Seems to me that saving power while adding a bunch of refrigerators sort of cancels out the benefits. Am I missing something here?
2.3 / 5 (3) Mar 08, 2010
superconducting DC (alternating current)


I agree with Royale. Also what if the power line gets cut and spews liquid nitrogen everywhere? Even if they put them underground, a hapless digger could hit one and get a facefull of LN2.
5 / 5 (2) Mar 08, 2010
I could see it being worthwhile in urban areas where very large amounts of electricity are moved about.

I remember seeing results a few years back that showed superconducting conduits could handle the same amount of power as 5 of their non-superconducting counterparts.

So perhaps when considering the higher load that the superconducting conduits can take, and the lower amount of loss, it just might be feasible.

There'd be a few more variables too, such as if the city has a reliable tunnel system to place the conduits in. And known active earthquake areas would have a harder time at providing that level of reliability.

If we can find a better way to cool them, then that would be great. Who knows. At least progress _is_ being made.
5 / 5 (1) Mar 08, 2010
is it worth it in the cost of cooling liquid nitrogen down.

Depends on how much power you want to tranfer. For high end users with powerplants nearby (think big manufacturing plants like auto makers, steel plants, paper mills, glass manufacturing, ... ) it would make sense.

It's pobably not commercially viable for long range transmission lines.

Also what if the power line gets cut and spews liquid nitrogen everywhere?

What of it? It evaporates and is non-toxic. As long as you don't persistently stand in the way you can even walk through a spray of liquid nitrogen (or dip your hand in it) without taking harm. If it's manufactured in sections then not much nitrogen would leak, anyways (and you want to have it in sections to prevent quenching like in early MRs which also use superconducting wires)

The coolant is also at the core of the system (you'd have to cut clean through to get at that)
not rated yet Mar 08, 2010
Why not use solid state Peltier coolers to keep the nitrogen cold? They could be powered by the main electric line. This is a fun game!
1 / 5 (1) Mar 08, 2010
possible benefits ?
- lets say they ever actually use 7% of the land in AZ for a solar farm and there is enough electricity to power the country -- how do you get that energy to NY ... You would need orders of magnitude of more energy to transmit it across the states -- this was just a far reaching example -
- storing energy (voltage - or - potential ) at night time in a closed loop , like during the summer when a/c is on at noon but the demand on the grid is lower at night, the power company could use a superconducting loop or grid as a giant battery

- main issue while a high voltage can be stored effeciently, superconducting does not lend it self well to super high current. I read this is a diferent article and I am still trying o come to terms with the concept.
5 / 5 (1) Mar 08, 2010
It seems to me that if it is possible to keep this new cable cold enough with liquid nitrogen that if you were to make a loop of it it would be then able to be used as an energy store (as current will flow indefinitely without loss in a superconductor) with much less cost than with other superconductors. This would have a huge impact on renewable energy as storage is the key for baseload renewables. I dont understand why research into this storage potential is neglected as we are better at making insulating systems than superconductors so even current 'high temperature' ones should work with a cleverly designed insulation system and not be stupidly expensive.
5 / 5 (1) Mar 08, 2010
No one seems to have noticed the error. DC means "Direct Current" not Aternating Current as mentioned at the start of the article, even when in brackets. This makes the second para confusing. Does the writer even know what they are talking about.
not rated yet Mar 08, 2010
What the article does not mention are the costs of supercooling the cable against the potential gain in power generation. The old adage "you cant get anything for nothing" applies. or as we would say here in Stoke on trent *you cant get owt for nowt"
not rated yet Mar 08, 2010
There's a much better Room Temperature Superconductivity technology that's been available for years but actively ignored -

The thought that power transmission companies want to reduce their line loss is just so much BS. Been there done that. DE
not rated yet Mar 08, 2010
Another problem is that DC (direct Current) cannot be transformed to different voltages easily or cheaply. In todays world multiple voltages are the norm. Imagine trying to run a computer circuit board with high voltage DC. Check the number of different voltages used in todays high tech living.
not rated yet Mar 08, 2010
A black cable in the sun? You'd need really good insulation.
4 / 5 (1) Mar 09, 2010
@Ant - unstated but assumed is that the amount of power required to keep the line cool is less that would be lost by resistance. Properly insulated, liquid nitrogen stays liquid (keeps its temperature) for quite some time - again the article does not state that the wire is thermally insulated, but it would be foolish not to insulate the wire. The wire is not a heat source - the article implies that a major source of heat transfer is where the superconducting cable meets ordinary cable, but that is solved by their "Peltier Current Lead".

The whole idea behind this technology is to **transport** power distances with minimal loss. Usually AC is used because resistive losses are less with AC - but when you don't have that type of loss DC is more efficient.

Technology is fairly advanced and readily available to convert DC into AC for voltage stepping and point of use.

1 / 5 (1) Mar 09, 2010
Rest assure all that this system will not go is crucial however to develop the architecture to aid the adaptation of mainstream conceivable future super conducing power line systems. Liquid nitrogen self contained sections keep everything superconducting, if there's a leak you replace the section where the leak is...forget fixing it not really plausible.
not rated yet Mar 09, 2010
The solution to our energy problems may be more technology not less. What will the Greens get exercised over then?
not rated yet Mar 09, 2010
The point is that the amount of N2 used is not proportional to the amount of power transmitted. So while the cost of the N2 loss/replacement goes up, the amount of power transmission goes up by a lot more.

The best thing about DC power transmission is that losses are far less when transmitting it underground. Of course it would need to be transformed to AC at some point, but if the source is solar, it can be transmitted without conversion for a long ways.
not rated yet Mar 09, 2010
the article does not state that the wire is thermally insulated,

The picture does.

Another advantage with using superconducting cables is that you can use much thinner cables because the power density (Amps per centimeters squared) can be much higher. The cooling will draw a constant amount of power. I guess we'll have to look at the cost benefit analysis - but with power losses being what they are for conventional wires I can imagine that there is a viable break-even point.

If they add a small vaccuum insulation layer this could well be efficient (if somewhat expensive to manufacture)
5 / 5 (1) Mar 09, 2010
I think this would work well in places that could use the space saving potential. read Manhattan. Or, really any city where huge amounts of power are moved around in a small area. I actually really enjoy this discussion guys. See, we can have a nice discussion without anyone yelling at another.
not rated yet Mar 13, 2010
I think this would work well in places that could use the space saving potential. read Manhattan.
A search is worth 1000 posts:
This tech is already being used in NYC and apparently elsewhere for AC transmission.
4 / 5 (1) Mar 13, 2010
What you all are missing is that when you lose refrigeration on a superconducting power conductor under load, it blows up. Duh! All that power has to go somewhere and when the conductor goes normal (stops being a superconductor) it has much higher resistance than copper. The conductor rapidly heats up and blows up. Its amazing what hundreds of megawatts do when used for heating and have no where else to go. No, you can't use Peltier coolers ... they are not capable of reaching the necessary temperatures and delivering sufficient wattage at those temperatures. The only thing superconductivity is useful for is magnets and passive RF components. I know, as I ran the engineering dept of a superconducting technology for a while and saw first hand what you can and cannot do. We had a lot of money, both government and private, to work with so cost was not the issue. The technology is just not suitable for this.
not rated yet Mar 14, 2010
That's why you construct such lines in sections (to avoid this 'quenching').

If you lose coolant in one section then only that section is affected. This is standard procedure in MR scanners which use superconducting coils.(also the LHC uses this type of setup)
1 / 5 (2) Mar 14, 2010
Much better is a true room-temp superconductor-or an analog- like kz1300club links to above. At one stroke, all the cooling requirements are eliminated, and we have lossless xmission over extended distance. Cost goes down across the board.
Unfortunately, my ingrained cynicism causes me to suspect that this is the main reason why this very technology has not been deployed, as it would lead to loss of profit in entire economic sectors.
Hell hath no Fury like a shareholder shorted.
not rated yet Mar 15, 2010
@antialias - they label "insulation', but don't specify thermal or electrical. You're probably right, it's thermal (and maybe electrical also).

I recently spoke with someone involved in low temp superconductor design for MRI systems. The wiring is designed such that normal conducting lines are intermixed in some way with the superconducting wires, so that if a quench occurred the current would dump into the conducting wires and things would have a good chance of not getting damaged - When MRI quenches it is often possible to restore the system without repairs, just re-cool/energize.

While MRI systems have limited energy, power transmission systems differ in that they have continual input of energy and while safety/continuance during a quench would likely be more challenging, I would imagine that engineers have taken that into account for this type of system as well - if the wire itself cannot handle the current once quenched there must be detection and switching to ordinary cable.

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